1. Field of the Invention
The present invention relates to hydraulic valve systems used, for example, in off-road earth moving, construction, and forestry equipment, such as rough terrain forklifts (also known as telehandlers), earth movers, backhoes, articulated booms, and the like. Hydraulic valve systems are utilized, for example, to cause pistons to lower, lift, extend, retract, lock, unlock, or angle a fork in a telehandler. The present invention relates to an improved design for such hydraulic valve systems.
2. Brief Description of the Related Art
Prior art hydraulic valve systems include the open center hydraulic valve system 110 illustrated in FIG. 1. The open center hydraulic valve system 110 in FIG. 1 is illustrated in a hydraulic circuit diagram in schematic form as would be understood by a skilled practitioner. The open center hydraulic valve system 110 of FIG. 1 presently is in common use, for example, in off-road earth moving, construction, and forestry equipment, such as telehandlers. FIG. 1 illustrates an example of an open center hydraulic valve system 110 for a telehandler.
While variations in the basic design of such a prior art open center hydraulic valve system 110 exist, the fundamental components and operation of such a system are briefly described below.
The prior art open center hydraulic valve system 110 of FIG. 1 typically includes one or more hydraulic fluid tanks 112, one or more constant flow open center hydraulic valve banks (“valves”) 114, and a fixed displacement pump 116 run by a motor 150 and driven by a motor shaft 152. (While the hydraulic fluid tanks 112 are illustrated in FIGS. 1-4 in multiple locations in the schematic illustrations for purposes of simplifying the illustration, skilled practitioners would recognize that the multiple illustrated locations of the hydraulic fluid tanks 112 in the schematics in FIGS. 1-4 would preferably constitute a single hydraulic fluid tank 112, or a system of hydraulically interconnected hydraulic fluid tanks 112, in actual operation). FIG. 1 illustrates a hydraulic system having one valve 114. For ease of reference, the valve 114 is separated into blocks A-F.
The valve 114, in turn, may include one or more spools 118, with each spool 118 being activated by spool actuators 120. The spool actuators 120 may be activated by an equipment operator using a number of known means, such as mechanically (for example, using a lever), electrically (for example, using a solenoid receiving an electrical signal from a switch, a joystick, a computer, or other means), electro-hydraulically, hydraulically, pneumatically, or otherwise. In the example illustrated in FIG. 1, the spools 118 in blocks B and C of valve 114 are activated by using electro-hydraulic valves 180, and the spools 118 in blocks D and E of valve 114 are activated by using a two-axis joystick 182.
In order to more understandably illustrate the operation of a spool 118 to selectively interconnect hydraulic pathways within a valve 114, a simplified drawing illustrating how a spool 118 of a simple prior art constant flow open center valve 114 is capable of redirecting the constant flow of hydraulic fluid is provided in FIG. 2. In the simplified drawing of FIG. 2, the well-known means of activating the spools 118 are omitted from the schematic diagram. Also omitted in FIG. 2 are ancillary hydraulic systems, such as the steering system 184 (including the steering/brake priority spool 186) and the brake system 188 (including the brake accumulator charge 190), which use relatively small amounts of hydraulic fluid flow/pressure compared to the remaining hydraulic functions, and the discussion of which is not pertinent to the invention herein.
In each of the blocks of the valve 114 illustrated in FIGS. 1 and 2, each spool 118 is capable of providing selective hydraulic communication with either one of a pair of associated hydraulic ports 122 and 124, depending upon the position of spool 118. The hydraulic ports 122 and 124 are hydraulically connected to a cylinder 126 on opposite sides of a piston 128. Each spool 118 has a number of internal hydraulic pathways which permit the spool 118, depending on its position, to direct hydraulic fluid flow to or from hydraulic ports 122 and 124, or to remain in a neutral (non-actuated) position wherein hydraulic fluid is permitted to flow unrestricted through the spool 118 through open center core 130.
Referring once again to the prior art open center hydraulic valve system 110 illustrated in FIGS. 1 and 2, each spool 118 is capable of selective hydraulic communication with a pair of associated hydraulic ports 122 and 124. Each pair of hydraulic ports 122 and 124, in turn, may be hydraulically connected to equipment applications in which the open center hydraulic valve system 110 is used to operate, typically utilizing a cylinder 126 and a piston 128. The hydraulic ports 122 and 124 selectively provide pressurized hydraulic flow to or from the cylinder 126 on opposite sides of the piston 128, thereby causing the piston 128 to move, and the application associated with the piston 128 to operate.
Referring again to FIGS. 1 and 2, each spool 118 of the valve 114, and, hence, each pair of hydraulic ports 122 and 124 associated with each spool 118, is associated with a function of the application on the equipment within which the open center hydraulic valve system 110 is utilized. In the example illustrated in FIG. 1, each one of the spools 118 (and the pair of hydraulic ports 122 and 124 associated with each spool 118) is associated with a block (indicated by a letter) in the valve 114, with each block, in turn, being associated with each of the following functions, which can be found, for example, in a telehandler: fork angle adjustment (block B), fork lock (block C), fork lift (block D), and fork extension (block E). Those functions are chosen for purposes of illustration, and, as would be recognized by skilled practitioners, those functions can vary, depending on the equipment and applications to which the open center hydraulic valve system 110 is assigned.
The valve 114 includes several hydraulic fluid pathways that may be selectively interconnected by activation of the spool 118, including an open center core 130, a power core 138, and a tank galley 132. The fixed displacement pump 116 pumps hydraulic fluid (at a constant flow rate for a given speed of the motor 150) from the hydraulic fluid tank 112 into the open center core 130. The tank galley 132 returns hydraulic fluid to the hydraulic fluid tank 112, where it is available to be re-pumped. The valve 114 also includes a hydraulic connection between the open center core 130 and the power core 138, namely, an open center/power core passage 140, upstream of the spools 118. (As commonly used, and as used herein, “upstream” shall mean in the direction towards a pump, “downstream” shall mean in the direction away from a pump). Typically, the valve 114 may also include smaller internal valves utilized to prevent, for example, overpressure or incorrect flow direction in the system, such as relief valves 142, or load drop check valves 144, which are not material to the explanation of the prior art or the invention.
The prior art open center hydraulic valve system 110 is typically housed in a standard manifold (not illustrated) attached to the equipment in which the open center hydraulic valve system 110 is being used. The fixed displacement pump 116 is typically driven by a motor 150, powered by a source such as by a power take-off (not illustrated), which, in turn, may be is directly mounted to a transmission (not illustrated), which, in turn, may be connected to the prime mover of the equipment in which the prior art open center hydraulic valve system 110 is being used.
The operation of the spools 118 in the valve 114 to direct hydraulic fluid flow to and to permit fluid flow from associated hydraulic ports 122 and 124 to cause, for example, a piston 128 to move within a cylinder 126 and thereby cause movement of a functional aspect of the equipment on which the open center hydraulic valve 110 is mounted is well-known to skilled practitioners, and can be ascertained by skilled practitioners by reference solely to the schematic diagrams found in FIGS. 1 and 2. For purposes of the following explanation, each of the hydraulic ports 122 and 124 will be assumed to be hydraulically connected to a cylinder 126 on opposite sides of a piston 128, respectively, in a manner similar to that illustrated in FIGS. 1 and 2.
As can be seen in FIGS. 1 and 2, and as will be described further below, when a spool 118 is caused or permitted by spool actuator 120 to be in the neutral position (with the open center core 130 unrestricted by the spool 118, and the fluid passageways between either the power core 138 or the tank galley 132, on the one hand, and the pair of hydraulic ports 122 and 124 associated with the spool 118, on the other hand, being obstructed by the spool 118), no net hydraulic fluid flows to or from the hydraulic ports 122 and 124 to the cylinder 126 on either side of the piston 128, and thus, the piston 128 associated with that spool 118 does not move. Instead, if all of the spools 118 in the valve 114 are in the neutral position, the hydraulic fluid delivered at a constant flow rate (for a given speed of motor 150) by the fixed displacement pump 116 flows unrestricted through the open center core 130 and through the open center of the other spools 118 to the tank galley 132 and to the hydraulic fluid tank 112 where it is re-pumped. (The power used to pump the unused hydraulic fluid flow is, in that case, effectively a loss). Hence, the functions to which the pistons 128 and cylinders 126 are associated (e.g., the height of the fork, as illustrated in block D) do not change, because there is no net change in hydraulic fluid in the cylinders 126 on either side of the pistons 128. The pistons 128 therefore do not move.
Once again referencing FIGS. 1 and 2, when a spool actuator 120 is activated by an operator (using electro-hydraulic valves 180 for spools 118 in blocks B or C for the fork angle adjustment or the fork lock, on the one hand, or using a joystick 182 for spools 118 in blocks D or E for the fork lift or the fork extension, on the other hand) to cause the associated spool 118 to move from the neutral position to a first non-neutral position, the activated spool 118 in the first non-neutral position restricts (partially or fully, depending on the design of the spool 118) the flow of hydraulic fluid pumped by the fixed displacement pump 116 through the open center core 130. The constant flow of hydraulic fluid delivered by the fixed displacement pump 116 is caused by the restriction by the spool 118 of the open center core 130 to increase in pressure. Referring to FIG. 1, the increase in fluid pressure upstream of the activated spool 118 in the open center core 130 is communicated hydraulically to the power core 138 through the open center/power core passage 140. The activated spool 118 also directs pressurized hydraulic fluid to flow from the power core 138 to a pre-selected one of the two hydraulic ports 122 or 124 associated with the activated spool 118 into the cylinder 126 on a first side of the piston 128. The activated spool 118 simultaneously allows fluid to flow out of the cylinder 126 through the other of the two second hydraulic ports 122 or 124 associated with the activated spool 118 which is connected on a second side of the piston 128. That hydraulic fluid then flows through the tank galley 132 to the hydraulic fluid tank 112 (where it is available to be re-pumped).
Thus, the net effect is that hydraulic fluid under pressure flows into the cylinder 126 associated with the activated spool 118 on the first side of the piston 128, and hydraulic fluid flows out of the cylinder 126 on the second side of the piston 128. This causes the piston 128 and any associated load to move toward the second side of the piston 128 associated with the activated spool 118 and the function to change (for example, in the case where the activated spool 118 is in block D associated with the fork lifting function, it would cause the fork to, e.g., rise). Any hydraulic fluid unused by the activated spool 118 flows through the restriction in that spool 118 via the open center core 130 to be either utilized by remaining downstream spools 118, or to then flow through the tank galley 132 to the hydraulic fluid tank 112.
On the other hand, if, as illustrated in FIGS. 1 and 2, the equipment operator manipulates the actuator 120 to cause the spool 118 to move from the neutral position to a second non-neutral position, that once again causes a restriction of the open center core 130, and causes the fluid flowing through the open center core 130 to increase in pressure. That increase in hydraulic pressure is once again communicated from the open center core 130 to the power core 138 through open center/power core passage 140. At the same time, hydraulic fluid is permitted by the activated spool 118 to flow out of the cylinder 126 on a first side of the piston 128 through a selected one of the two connected hydraulic ports 122 or 124 associated with activated spool 118 and through the tank galley 132 to the hydraulic fluid tank 112. Also at the same time, the activated spool 118 directs pressurized hydraulic fluid (under pressure due to restriction of the opening in the open center core 130 by the activated spool 118) to flow from the power core 138 through the other of the associated hydraulic ports 122 or 124 into the cylinder 126 on a second side of the piston 128.
Thus, hydraulic fluid under pressure is introduced to the cylinder 126 on a second side of the piston 128, and hydraulic fluid is drained from the cylinder 126 on a first side of the piston 128. This causes the piston 128 to move toward the first side of the piston 128 and the equipment function to change (for example, in the case where the activated spool 118 is in block D associated with the fork lifting function, it would cause the fork to, e.g., lower). Once again, any hydraulic fluid unused by the activated spool 118 would flow through the restriction in the spool 118 via the open center core 130 to be either utilized by remaining downstream spools 118, or to then flow through the tank galley 132 to the hydraulic fluid tank 112.
A skilled artisan would recognize, of course, that this activation of spools 118 in the valve 114 can be utilized to operate a number of different equipment functions having moving components, and would not be limited to fork lifting (or to telehandlers).
Further details of the operation of the prior art open center hydraulic valve system 110 illustrated in FIG. 1 are described below. The explanation herein concerning the operation of a single spool 118 (and its associated pair of hydraulic ports 122 and 124) within a single valve 114 associated with a particular single function is illustrative, and is not limited to that particular single spool 118 or valve 114, and applies to other spools 118 within the open center hydraulic valve system 110 as well.
Because the pump for the prior art open center hydraulic valve system 110 is a fixed displacement pump 116, the flow of the hydraulic fluid supplied by the fixed displacement pump 116 is constant for a given speed for the motor 150 on the equipment in which the prior art open center hydraulic valve system 110 is mounted.
When the activators such as the electro-hydraulic valves 180 and the joystick 182 associated with the spool actuators 120 for the valve 114 in the prior art open center hydraulic valve system 110 are in the neutral position, all of the associated spools 118 are likewise in the neutral position. As illustrated in FIG. 1, the centers of the valve spools 118 are open, the net flow paths to the associated hydraulic ports 122 and 124 (from the open center core 130 or the power core 138), or from the hydraulic ports 122 and 124 (to the tank galley 132), are blocked by the spools 118, and all net hydraulic fluid flow pumped by the fixed displacement pump 116 from the hydraulic fluid tank 112 at a constant flow rate through the open center core 130 flows unrestricted through the open center core 130 through the spools 118 to the tank galley 132 and then back to the hydraulic fluid tank 112, where it is again available to be re-pumped.
When one of the functions associated with the prior art open center hydraulic valve system 110 is desired to be activated, the spool actuator 120 associated with that function is activated by an equipment operator using an activator such as an electro-hydraulic valve 180 or a joystick 182 in order to move the associated spool 118 (upwards or downwards, or from side to side, as shown in the schematics in FIGS. 1 and 2) in order to restrict the opening through the open center core 130 to the tank galley 132. This restriction of hydraulic fluid flow by the activated spool 118 in the open center core 130 increases the pressure of the hydraulic fluid in the open center core 130 being provided at a constant flow rate by the fixed displacement pump 116 upstream of the activated spool 118. The resulting increased hydraulic fluid pressure in the open center core 130 upstream of the activated spool 118 is transmitted hydraulically through the open center/power core passage 140 to the power core 138.
Assuming that the hydraulic port 122 associated with activated spool 118 is connected to the associated cylinder 126 on a first side of piston 128, and associated hydraulic port 124 is connected to that cylinder 126 on the second side of piston 128, and referring to FIGS. 1 and 2, if the chosen spool actuator 120 is activated with the intention of causing the associated piston 128 to move to a first non-neutral position (and to thereby, in the example described above of the spool 118 associated with block D, lift a fork and any associated load), then not only is the open center core 130 restricted to cause an increase in pressure to occur in the open center core 130 upstream of the activated spool 118 and be transmitted via the open center/power core passage 140 to the power core 138, but the spool 118 at the same time opens a hydraulic passage in the valve 114 between associated hydraulic port 122 (hydraulically connected to a cylinder 126 at a first side of the piston 128, in the manner illustrated in FIGS. 1 and 2) and the power core 138. The hydraulic fluid, having increased hydraulic pressure in the power core 138, is transmitted through associated hydraulic port 122 to the cylinder 126 on the first side of the piston 128. Simultaneously, activated spool 118 opens a hydraulic passage in the valve 114 between associated hydraulic port 124 (hydraulically connected to a cylinder 126 at a second side of the piston 128, in the manner illustrated in FIGS. 1 and 2) and the tank galley 132. The result is that hydraulic fluid under pressure from the power core 138 flows through associated hydraulic port 122 and begins filling the cylinder 126 on the first side, e.g., below the piston 128, and hydraulic fluid is permitted to leave the cylinder 126 on the second side, e.g., above the piston 128 by flowing through associated hydraulic port 124 into the tank galley 132 to return to the hydraulic fluid tank 112, where it is available to be re-pumped. By adding sufficiently pressurized hydraulic fluid to the cylinder 126 below the piston 128, and by reducing hydraulic fluid in the cylinder 126 above the piston 128, the piston 128 (and, in the example described above, the attached fork and its associated load) is lifted.
Conversely, if the chosen spool actuator 120 is activated with the intention of causing the piston 128 to move to a second non-neutral position (and to thereby, in the example of the spool 118 associated with block D, cause a fork to lower), then not only does the activated spool 118 cause the open center core 130 to be restricted to cause an increase in fluid pressure in the open center core 130 upstream of activated spool 118 to be hydraulically transmitted to the power core 138 via open center/power core passage 140, but also the activated spool 118 opens a hydraulic passage in the valve 114 between the associated hydraulic port 124 (hydraulically connected to cylinder 126 at a second side of the piston 128) and the power core 138 (having pressurized hydraulic fluid). Simultaneously, the activated spool 118 opens a passage in valve 114 between associated hydraulic port 122 (hydraulically connected to cylinder 126 on a first side of the piston 128), and the tank galley 132, allowing hydraulic fluid to flow out of the cylinder 126 from the first side of the piston 128 to the tank galley 132 and the hydraulic fluid tank 112. The result is that hydraulic fluid under pressure from the power core 138 begins filling the cylinder 126 on the second side, e.g., above, and hydraulic fluid begins leaving the cylinder 126 on the first side, e.g., below, thereby causing the associated piston 128 (and, in the above example, the attached fork and its associated load) to lower.
When the open center hydraulic valve system 110 is used to operate a function on the equipment on which it is mounted, hydraulic pressure must be built up in the open center core 130 (which, as previously discussed, is then communicated via the open center/power core passage 140 to the power core 138, and then to one of the two hydraulic ports 122 or 124 associated with that function) sufficient to match the load for the function. In the example described above of an open center hydraulic valve system 110 used on a telehandler, with the raising or lowering of the fork lift function being associated with the spool 118 of block D of valve 114, for instance, the hydraulic pressure developed in the open center core 130, which is then delivered to the selected one of the two hydraulic ports 122 or 124 associated with block D must be sufficient to move associated piston 128, the fork attached to the piston 128, and the load on the fork, all under precise operator control. This is accomplished by the operator manipulating the activators (in the example discussed above for block D of valve 114 for raising or lowering the fork, the relevant activator would be movement of the two-axis joystick 182 in the horizontal direction as illustrated in FIG. 1) to activate the associated spool actuator 120 for the spool 118 in block D so as to cause the spool 118 in block D to restrict the flow of hydraulic fluid provided by the fixed displacement pump 116 (at a constant rate for a given motor speed) through the open center core 130. This restriction by the associated spool 118 of the hydraulic fluid flow through the open center core 130 causes the hydraulic pressure to increase upstream of the activated spool 118. That increase in hydraulic pressure is transmitted to the open center/power core passage 140, then to the power core 138, and then through the activated spool 118 to the selected one of the two hydraulic ports 122 or 124 associated with the activated spool 118, as determined by the operator.
In the example previously discussed, where the operator was operating a joystick 182 to activate the raising of the fork function associated with block D of valve 114, the operator would cause the activated spool 118 to move to a first non-neutral position which would restrict the flow of hydraulic fluid to the point that sufficient hydraulic fluid pressure has been built up in the power core 138 and delivered to hydraulic port 122 (while at the same time allowing hydraulic fluid to drain from hydraulic port 124 to the tank galley 132 and then to the hydraulic fluid tank 112)—that is, sufficient hydraulic pressure would be generated to raise associated piston 128, the attached fork, and any associated load on that fork. Unless and until the operator had caused sufficient hydraulic pressure to be generated by the flow restriction caused by the activated spool 118, the fork and any associated load would not, of course, be raised. Stated another way, when any of the functions associated with valve 114 are operated, hydraulic pressure must be built up in the power core 138 to match the load associated with the chosen functions.
During the operation of the chosen functions, the operator often requires quick movements and fine control. In addition, the operator often executes more than one function associated with the valve 114 simultaneously. Furthermore, different functions and different movements associated with a function require different hydraulic pressures. In the example discussed above for the valve 114 associated with a telehandler, for instance, the fork lifting and fork extension functions (blocks D and E) require considerably more hydraulic pressure than the fork angle and fork lock functions (blocks B and C). Additionally, different movements of functions require more hydraulic pressure than others. For instance, raising the fork with a load requires more hydraulic pressure than lowering the fork with a load. Moreover, even similar movements of the same function may require different hydraulic pressures depending upon different conditions. For example, raising the fork may require more or less hydraulic pressure depending upon the fork position or weight of the load being raised.
As discussed above, operation of the fork angle and fork lock (blocks B and C, FIGS. 1 and 2) require considerably less amounts of hydraulic pressure than the fork lifting and fork extension functions (blocks D and E, FIGS. 1 and 2), and therefore are not discussed further. Similarly, operation of the brake system 188 and the steering system 184 (FIG. 1) require relatively small amounts of hydraulic pressure, and can be effectively disregarded for purposes of further discussion of the valve 114. They have been removed from FIG. 2 for purposes of clarity.
In practice, during the operation of equipment commonly utilizing valve 114, such as the telehandler example discussed above, the operator of the equipment will activate several functions simultaneously. In the example of the telehandler, the fork lifting and fork extension functions (blocks D and E of FIGS. 1 and 2) are often operated simultaneously, frequently using a two-axis joystick 182 (see FIG. 1). For instance, the operator may simultaneously lift and extend the fork arm so that the load on the fork follows a substantially vertical trajectory. In the open center hydraulic valve system 110 illustrated in FIGS. 1 and 2, if the operator simultaneously activates several functions, especially including the fork lifting and fork extension (blocks D and E), the equipment will not respond as the operator commanded. Generally, the fork extension function (block E) requires a lower hydraulic pressure in the hydraulic fluid than does the fork lifting function (block D). On the other hand, in hydraulic systems, absent some compensation in the system design, the flow of hydraulic fluid follows the path of least resistance (i.e., the path in which the pressure is lowest). Consequently, in order for an operator to control both functions (fork lifting and fork extension), the operator is required to utilize the activator (e.g., joystick 182) in a manner to meticulously meter the flow of hydraulic fluid through the extension function (block E of valve 114) creating a power loss. Furthermore, the controllability that can be attained using that technique is not very high and depends considerably on the ability and skills of the operator, because the two hydraulic pressures to be delivered to the functions are dependent on the load and fork position (extension, height, and angle), which change.
In order to overcome the issues discussed above with respect to the open center hydraulic valve system 110, and to establish better equipment controllability, load sensing anti-saturation systems have been used. Such a system, however, is much more complicated and much more costly, because it requires the introduction of a variable displacement pump and flow/pressure compensators. Consequently, this potential alternative has been largely deemed unacceptable as being more difficult to maintain and somewhat cost prohibitive.
The present invention, known as a smart flow sharing system, overcomes the problems associated with both the prior art open center hydraulic valve system 110 and the potential alternatives that have been considered and largely rejected in many applications (for example, the load sensing anti-saturation system). The smart flow sharing system provides a relatively uncomplicated and cost-effective alternative hydraulic system that achieves superior controllability for the operator of the equipment on which it is installed.